1. Field of the Invention
The present invention relates to a fundus camera for photographing an ocular fundus of a subject's eye.
2. Description of the Related Art
In order to obtain a clear image of a blood vessel or the like, such a fundus camera is in practical use that an ocular fundus is illuminated through a dedicated narrow-bandwidth bandpass filter, which is referred to as a red free filter, to form a monochromatic image from a color image captured by a color image capture element according to a calculation processing.
Japanese Patent Application Laid-open No. 2003-93336 discusses an electronic endoscope device which produces an effect of a pseudo narrow-bandwidth bandpass filter from a typical RGB color image without providing a dedicated narrow-bandwidth bandpass filter.
In a fundus camera using a red free filter, upon photographing, the dedicated narrow-bandwidth bandpass filter is required and a system for inserting the narrow-bandwidth bandpass filter into an optical path of an illumination unit is also required. Consequently, such a problem arises that the fundus camera using the red free filter comes to have a complex configuration and is expensive.
In Japanese Patent Application Laid-Open No. 2003-93336, since a subject to be examined is a human body, it is premised that a spectral reflectance of the human body is almost constant. However, in Japanese Patent Application Laid-Open No. 2003-93336, it is not generally possible to obtain a specific spectral characteristic from an RGB color image. This is because, there is a case that, even when a color is viewed as the same color as the other color on the RGB color image, the color is actually the color similar to the other color depending on a metamerism caused due to a plurality of wavelengths upon photographing. The metamerism is a phenomenon that physically different colors are viewed as the same colors. For example, if red light and yellow light are extracted from light having various wavelengths and spectrums and are mixed together, thus mixed light becomes an orange color. However, the mixed orange color is a light physically different from an orange color of a single wavelength.
Therefore, a conventional apparatus has an advantage that no optical filter switching system or dedicated filter is required. However, conventional system has a mere pseudo narrow-bandwidth bandpass filter, so that there may be cases that the effect thereof is not sufficient enough with respect to the system using an optical filter, and further no effect can be produced in a specific lesion.